The present invention relates to a hydraulic braking circuit fitted with a master brake cylinder and a wheel-antilock device for a motor vehicle and, more particularly, to a circuit of this type fitted with means for isolating wheel brakes from the master brake cylinder during the operation of the antilock device.
FR-A-2,611,630 describes a braking circuit of this type comprising a master brake cylinder actuated by a servo-brake controlled by a pedal, a brake associated with each wheel of the vehicle, a solenoid valve for closing the braking circuit under normal conditions and, under the control of the antilock device, for relieving the pressure in a wheel brake by placing the latter in communication with means for storing the brake fluid of the circuit. In addition to means making it possible to filter out reactions which are unpleasant for the driver on the brake pedal during the operation of the antilock device, the circuit comprises a controlled valve which is sensitive to the relief of the pressure in the wheel brake in order to release the closure of the supply circuit of this brake by a restriction which slows down the rise in pressure of the fluid in the circuit. Phases of slow pressure rises of this type occur during the operation of the antilock device, as is well known.
The circuit described in the above-mentioned document meets the stated objectives but, nevertheless, has some disadvantages. During the operation of the antilock device, the level of noise from the high-pressure delivery pump may become very considerable. Moreover, the pressure variations are returned to the master brake cylinder and give rise to pulsations of the brake pedal, a phenomenon which is difficult to control. Lastly, it has been noticed that, during the operation of the antilock device, fluctuations in pressure occur in the phases of a rise in pressure, fluctuations which are felt by the master brake cylinder, and hence the brake pedal.